Great Moments in TV Cameos: Boyz II Men, on "How I Met Your Mother," Singing The Slap Song (Video)

Those watching How I Met Your Mother last night got a decent surprise at the very end of the episode: Boyz II Men, singing "You Just Got Slapped"—otherwise known as "The Slap Song"—at the end of the episode, alongside HIMYM's cast.

Some background on how we got here:

A recurring episode theme on How I Met Your Mother has been the Slap Bet. Basically, Barney (Neil Patrick Harris) lost a bet to Marshall (Jason Segal) in the eighth episode of the second season of the show over whether or not Robin (Cobie Smulders) was a Canadian porn star in a past life. The winner of the bet gets to slap the loser as hard as they can.

The episode, handily one of the best sitcom episodes ever, got a few sequels (because, over the course of the bet, Barney ends up indebtted eight slaps to Marshall). In the third season, there was "Slapsgiving."

In that episode, after slapping him incredibly hard, Marshall sings Barney a song about getting slapped. Because it's Jason Segal doing the singing—he of the Forgetting Sarah Marshall vampire musical—it's kind of great:

In the fifth season, there was "Slapsgiving 2." Then there was "Slapsgiving 3." A bunch of other slaps were doled out between all of this. So the only logical conclusion to the Slap Saga of How I Met Your Mother was Boyz II Men, singing a song about slapping Neil Patrick Harris in the face, after an episode that was essentially a tribute to Kill Bill Part 2, about slapping Neil Patrick Harris in the face.

And here it is:

The episode was as weird and bizarre and hilarious as the above, and the show—in its final season—is going for broke with most of its final showings; most of them aren't as divisive as this, but you've got to admire the followthrough and outright commitment to weirdness, especially on a sitcom, especially in 2014. Not bad.